Rosiglitazone maleate, 5-[4-[2-(N-methyl-N-(2-pyridyl)amino)ethoxy]benzyl]thiazolidine-2,4-dione maleate, has the following general structural formula:

Rosiglitazone is a member of the thiazolidinedione class of compounds and is one of the most potent compounds of this class. The thiazolidinedione class of antidiabetics, such as pioglitazone, englitazone, rosiglitazone, troglitazone and ciglitazone, has been shown to alleviate insulin resistance in humans. Rosiglitazone is, therefore, a known antidiabetic compound, and more particularly is the preferred drug for non-insulin dependent diabetes mellitus (NIDDM). Diabetes mellitus is a complex, chronically progressive disease, which affects the function of the kidneys, eyes, vascular and nervous systems.
EP 0306228B describes the synthesis of 5-[4-[2-(N-methyl-N-(2-pyridyl)amino) ethoxy]benzylidene]thiazolidine-2,4-dione,

by condensing 4-[2-(N-methyl-N-(2-pyridyl)amino)ethoxy]benzaldehyde (which is an impure oil),

with 2,4-thiazolidinedione, to obtain above 5-[4-[2-(N-methyl-N-(2-pyridyl)amino) ethoxy]benzylidene]thiazolidine-2,4-dione, which is then reduced with Pd/C to obtain rosiglitazone free base. We have now developed an improved synthesis of rosiglitazone, or a pharmaceutically acceptable salt thereof, which alleviates many problems associated with the prior art preparation of rosiglitazone substantially as hereinafter described in greater detail.